NAME: keep_compatibility
PURPOSE:
1) define key_forgetold = 1b - keyword_set(flag)
2) remove all oldcm_used.pro found in !path
3) define and create myuniquetmpdir and add it to !path
4) copy oldcm_full(_empty) to myuniquetmpdir+'oldcm_used.pro'
CATEGORY: compatibility with old version
CALLING SEQUENCE:keep_compatibility [, flag]
INPUTS:
flag: 1 or 0 to keep or forget the compatibility
dir: the directory where we create oldcm_used.pro.
if omitted, is automatically defined to
1b - keyword_set(key_forgetold)
COMMON BLOCKS: cm_general
SIDE EFFECTS: see purpose
RESTRICTIONS: copy oldcm_full or oldcm_empty must be found in the
!path. dir must aslo be in the !path